perf evsel: Rename perf_evsel__group_desc() to evsel__group_desc()

As it is a 'struct evsel' method, not part of tools/lib/perf/, aka
libperf, to whom the perf_ prefix belongs.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/ui/gtk/hists.c

@@ -646,7 +646,7 @@ int perf_evlist__gtk_browse_hists(struct evlist *evlist,
 				continue;
 
 			if (pos->core.nr_members > 1) {
-				perf_evsel__group_desc(pos, buf, size);
+				evsel__group_desc(pos, buf, size);
 				evname = buf;
 			}
 		}